1. Field of the Invention
The present invention relates to a double-meshing-type silent chain drive having a silent chain capable of meshing with sprockets located inside and outside the chain and also to a sprocket for use in the double-meshing-type silent chain drive.
2. Description of the Related Art
Conventionally, in some cases, a double-meshing-type silent chain capable of meshing with sprockets or toothed pulleys which are mounted on respective driven shafts located inside and outside the chain is used as a timing chain for transmitting rotational motion from the crankshaft of an engine to the cam-shaft of the engine or to the shaft of an auxiliary device such as an oil pump. A double-meshing-type silent chain is employed when driven shafts located inside and outside the chain must be rotated in opposite directions.
FIG. 17 shows a conventional double-meshing-type silent chain. In FIG. 17, an endless chain A1 meshes with a sprocket A2 located inside the chain A1 as well as with a toothed pulley A3 located outside the chain A1.
In the chain A1, links, each composed of three kinds of link plates having different shapes, are connected by pins A4. Specifically, guide link plates A5 are disposed at the widthwise outermost sides of the chain A1 as well as alternately along the longitudinal direction of the chain A1. As shown in FIG. 18, the guide link plate A5 has a straight edge portion a formed at the inner circumferential side of the chain A1 and two small meshing teeth b which are formed at the outer circumferential side of the chain A1 to be located at longitudinally opposite end portions of the guide link plate 5. The small meshing teeth b mesh with the toothed pulley A3.
A link plate A6 is pin-connected with adjacent guide link plates A5 at opposite end portions thereof such that the link plate A6 is in contact with inside faces of the guide link plates A5. The link plate A6 has two meshing teeth c formed at the inner circumferential side of the chain A1 so as to mesh with the sprocket A2, as well as two small meshing teeth b formed at the outer circumferential side of the chain A1 so as to mesh with the toothed pulley A3.
Plates A7 and A8 each have two meshing teeth c formed at the inner circumferential side of the chain A1 so as to mesh with the sprocket A2, as well as a flat back face d formed opposite to the meshing teeth c.
Notably, the meshing teeth c formed at the inner circumferential side of the chain A1 and the teeth of the sprocket A2, which mesh with the meshing teeth c, employ a standard tooth profile. By contrast, the meshing teeth b formed at the outer circumferential side of the chain A1 and the teeth of the toothed pulley A3, which mesh with the meshing teeth b, employ a non-standard tooth profile.
The above conventional double-meshing-type silent chain employs three kinds of link plates having different shapes. Thus, in a step of manufacturing plates, link plate dies corresponding to the different link plate shapes must be used. Also, in an assembling step, a large number of kinds of component parts must be handled and controlled. As a result, manufacturing cost is high.
Also, since the profile of the meshing teeth formed at the outer circumferential side of the chain is smaller than the standard tooth profile, when a large load torque acts on the toothed pulley located outside the chain, the toothed pulley disengages from the chain and slips along the chain. Thus, a maximum torque that can be transmitted to the toothed pulley is smaller than that which can be transmitted to the sprocket located inside the chain. This significantly limits the selection of a device to be driven through engagement with the outer circumference side of the chain.
Further, the guide link plate has no meshing teeth at the inner circumferential side of the chain, but instead has the straight edge portion at the inner circumferential side of the chain. Consequently, the guide link plate is relatively heavy, causing an increase in the weight of the entire chain. This causes an increase in impact energy generated due to meshing engagement between the chain and the sprocket or between the chain and the toothed pulley when the chain travels, resulting in an increase in working noise.
Also, a heavy chain weight causes an increase in tension derived from a centrifugal force produced when the chain travels, accelerating wear of a shoe surface of a chain guide or the like as well as elongation of the chain. Particularly, when such a double-meshing-type silent chain is used as a timing chain for an engine, timing drive of the engine may be adversely effected.
An object of the present invention is to provide a double-meshing-type silent chain drive which solves the above-mentioned problems involved in the prior art, enables a reduction in manufacturing cost through improvement of productivity, and enables transmission of a strong driving force between a double-meshing-type silent chain and a sprocket meshed with the chain along the outer circumference thereof.
Another object of the present invention is to provide a sprocket for meshing with the double-meshing-type silent chain, which is capable of suppressing chain vibration while maintaining high transmission efficiency.
To achieve the above object, the present invention provides a double-meshing-type silent chain drive comprising a double-meshing-type silent chain and a sprocket for meshing with the chain. The chain includes link plates having the identical side profile. Each link plate has two meshing teeth and a flat back face formed opposite to the meshing teeth. Two kinds of links are alternately arranged in the longitudinal direction of the chain, while the adjacent links are connected by pins. In one kind of link, an odd number of the link plates are disposed in the width direction of the chain. In the other kind of link, an even number of the link plates are disposed in the width direction of the chain. In each link, the link plates are oriented such that the meshing teeth of link plates located at widthwise opposite ends project outwardly with respect to the chain and the meshing teeth of the remaining link plates project inwardly with respect to the chain.
In the double-meshing-type silent chain of the present invention, all of the link plates have the identical side profile. Also, the outermost link plates of each link are oriented such that their meshing teeth project outwardly with respect to the chain. Thus, these outwardly projecting meshing teeth are meshed with a sprocket disposed outside the chain to thereby transmit power between the chain and the sprocket.
In each link, all the link plates except the outermost link plates are oriented such that the meshing teeth project inwardly with respect to the chain. These inwardly projecting meshing teeth are meshed with a sprocket disposed inside the chain to thereby transmit power between the chain and the sprocket.
Since all of the link plates have the identical side profile, the link plates can be manufactured through use of a single kind of link plate die. As compared to the case of a conventional chain of this kind composed of link plates having a plurality of side profiles, man-hours required for control of component parts can be reduced, and erroneous assembly can be prevented, thereby greatly improving productivity.
In contrast to the case of a conventional silent chain, large heavy guide plates having no teeth are not used, thereby reducing the weight of the entire chain.
Further, since meshing teeth which project outwardly with respect to the chain are profiled similarly to those which project inwardly with respect to the chain, there can be increased a torque that can be transmitted between the chain and a sprocket disposed outside the chain.
Preferably, the double-meshing-type silent chain of the present invention is such that, in each link, the meshing teeth of some link plates oriented in one direction project beyond the back faces of the remaining link plates oriented in an opposite direction.
In this case, the shoe face of a chain guide or that of a tensioner lever can be brought into slidable contact with the back faces of the plates oriented outwardly with respect to the chain, while the opposite side faces of the shoe are guided along the inside faces of the meshing teeth of the opposed outermost link plates, which meshing teeth project outwardly beyond the plate back faces.
The sprocket may be a first-type sprocket for meshing with the double-meshing-type silent chain along the outer circumference thereof, wherein a plate support face is formed in each of meshing teeth of the sprocket so as to support the back faces of the link plates which are oriented outwardly with respect to the chain, during the sprocket meshing with the link plates whose meshing teeth are oriented outwardly with respect to the chain.
In the first-type sprocket, power transmission is achieved through engagement with the meshing teeth of the outermost link plates in each link. Also, the plate support face formed in each meshing tooth of the sprocket abuts on the back faces of the link plates which are oriented outwardly with respect to the chain, to thereby partially bear a reaction force of the running chain imposed on sprocket teeth and thus improve sprocket durability. Further, the plate support faces serve as a chain guide for guiding the back faces of link plates to thereby suppress chain vibration.
Since an existing standard sprocket can be used as the first-type sprocket by machining tip portions of sprocket teeth to form the plate support face in each sprocket tooth, the first-type sprocket can be manufactured at low cost and can be used with the double-meshing-type silent chain of the present invention.
The sprocket may also be a second-type sprocket for meshing with the double-meshing-type silent chain along the outer circumference thereof, comprising a plate-back-face support element and two meshing elements. The plate-back-face support element has a cylindrical surface that abuts on the flat back faces of the link plates which are oriented outwardly with respect to the chain. The meshing elements are integrally coupled with the plate-back-face support element such that the plate-back-face support element is interposed between the meshing elements. Meshing teeth are formed on the circumferences of the meshing elements concentrically with the cylindrical surface of the plate-back-face support element so that the meshing elements can mesh with the link plates whose meshing teeth project outwardly with respect to the chain.
In the second-type sprocket, the two meshing elements have meshing teeth which are formed on the circumferences and which are profiled so as to completely mesh with outwardly projecting meshing teeth of the chain. Therefore, when the second-type sprocket is meshed with the outer circumferential side of the double-meshing-type silent chain of the present invention, a large torque can be transmitted therebetween.
Also, in the second-type sprocket, the plate-back-face support element has a continuous cylindrical surface for contact with back faces of link plates. The continuous cylindrical profile establishes continuous and smooth contact with the back faces, thereby significantly suppressing chain vibration and partially bearing a reaction force of the running chain imposed on sprocket teeth to thereby lessen sprocket teeth load. Thus, sprocket durability can be improved.
The sprocket may be a third-type sprocket for meshing with the double-meshing-type silent chain along the outer circumference thereof. The sprocket includes a meshing element having meshing teeth formed on an outer circumference thereof for meshing engagement with the meshing teeth of the link plates which are oriented inwardly with respect to the chain, and two plate-back-face support elements provided concentrically on opposite sides of the meshing element and each having a cylindrical outer surface for abutment with the flat back faces of the link plates of the chain which are oriented inwardly with respect to the chain.
When the third-type sprocket is used for mesh with the double-meshing-type silent chain along the inner circumference thereof, the meshing teeth formed on the circumference of the meshing element are in mesh with the meshing teeth of the chain which are oriented inwardly with respect to the chain to achieve power transmission between the sprocket and the chain. At the same time, the respective cylindrical outer surfaces of the plate-back-face support elements provided on opposite sides of the meshing element abut on the flat back faces of the link plates which are oriented inwardly with respect to the chain to thereby support or bear reaction from the chain.
In the third-type sprocket, while the meshing teeth of the meshing element mesh with the meshing teeth of the chain oriented inwardly with respect to the chain to achieve power transmission, the plate-end-face support elements smoothly guide and support the flat back faces of the link plates to thereby achieve the function of a chain guide. Vibrations resulting form polygonal movement of the chain can be suppressed to thereby stabilize the travel condition of the chain and lower the operation noise.
It is preferable that when the cylindrical outer surface of each of the plate-back-face support elements is in abutment with the flat back faces of the link plates, the meshing teeth of the meshing element mesh with the meshing teeth of the opposing link plates at a position offset from a meshing pitch circle of the meshing teeth of the meshing element in a radial outward direction of the sprocket. With this arrangement, the cylindrical outer surfaces of the plate-end-face support elements forcibly displace the back faces of the link plates in a radial outward direction before the meshing teeth of the meshing element mesh with the teeth of the chain. With this displacement, the meshing teeth of the sprocket mesh with the meshing teeth of the chain at a position located outside the meshing pitch circle of the meshing teeth of the sprocket. Such meshing is particularly effective to reduce the load in the radial direction of the sprocket.
The sprocket may be a fourth-type sprocket which comprises a plate-back-face support element having a cylindrical outer surface for abutment with the flat back faces of the link plates of the chain that are oriented outwardly with respect to the chain, and two meshing elements provided concentrically on opposite sides of the plate-end-face support element and each having meshing teeth formed on an outer circumference thereof for meshing engagement with the meshing teeth of the link plates of the chain which are oriented outwardly with respect to the chain. The cylindrical outer surface of the plate-back-face support element is in abutment with the flat back faces of the link plates, and the meshing teeth of each of the meshing elements mesh with the meshing teeth of the opposing link plates at a position offset from a meshing pitch circle of the meshing teeth of the meshing elements in a radial outward direction of the sprocket.
In the fourth-type sprocket, the cylindrical outer surface of the plate-end-face support element forcibly displaces the back faces of the link plates in a radial outward direction before the meshing teeth of the meshing elements mesh with the teeth of the chain. With this displacement, the meshing teeth of the sprocket mesh with the meshing teeth of the chain at a position located outside the meshing pitch circle of the meshing teeth of the sprocket. Such meshing is particularly effective to reduce the load in the radial direction of the sprocket.
The sprocket may be a fifth-type sprocket for meshing with a double-meshing-type silent chain, which comprises two meshing elements each having teeth formed on an outer circumference thereof for meshing engagement with the meshing teeth of the link plates of the chain which are oriented outwardly with respect to the chain, a buffer-ring support element having a cylindrical outer surface and concentrically and integrally joining the two meshing elements, and a buffer ring having an inside diameter larger than the outside diameter of the buffer-ring support element and being floatingly fitted around the cylindrical outer surface of the buffer-ring support element while the buffer ring is prevented from moving in the axial direction between the two meshing elements. The buffer ring has an outer peripheral surface adapted to be in abutment with opposing flat back faces of link plates at positions in front and in rear of a meshing position at which the meshing teeth of the link plates are in mesh with the meshing teeth of the meshing elements. At the meshing position, the outer peripheral surface of the buffer ring is separated from the flat back faces of the link plates and an inner peripheral surface of the buffer ring is in abutment with the cylindrical outer surface of the buffer-ring support element.
When the fifth-type sprocket is used for meshing with the double-meshing-type silent chain along the outer circumference thereof, the outer peripheral surface of the buffer ring disposed between the meshing elements is first brought into abutment with the flat end faces of the link plates of the chain.
When the back faces of the link plates impinge on the outer peripheral surface of the buffer ring, the buffer ring is flexed or otherwise deformed in a floating manner around the buffer-ring support member to thereby absorb impact energy created at a collision. Thereafter, as the chain advances, the meshing teeth of the outermost link plates of each link reach the meshing position, the outer peripheral surface of the buffer ring disengages from the back faces of the link plates. At the meshing position, the inner peripheral surface of the buffer ring abuts on the cylindrical outer surface of the buffer-ring support element.
As the chain further advances, the outer peripheral surface of the buffer ring comes again into abutment with the opposing back faces of the link plates to thereby guide the chain such that the engagement between the meshing teeth of each meshing element and the meshing teeth of the corresponding link plates is released.
In the fifth-type sprocket, since the outer peripheral surface of the buffer ring fitted around the buffer-ring support element abuts on the back faces of the link plates in advance to the mutual meshing between the meshing teeth of the sprocket and the meshing teeth of the chain, vibrations of the chain arising from polygonal movement of the chain as the chain moves past the sprocket can be suppressed. At the same time, collision between the meshing teeth of the sprocket and the meshing teeth of the chain can be absorbed with the result that the operation noise of the chain while running is considerably reduced.
As the sprocket rotates, the buffer ring is caused to oscillate or wobble around the buffer-ring support element while it is rotating about its own axis. Thus, the position of collision between the meshing teeth of the sprocket and the meshing teeth of the chain changes at random, so that excess local wear of the tooth surfaces can be prevented.
Additionally, a lubricating oil supplied externally is guided by the buffer ring between the mutually intermeshing teeth of the chain and sprocket with the result that the teeth are protected against wear and fatigue and wear elongation of the chain is minimized.
The sprocket may be a sixth-type sprocket used for meshing with a double-meshing-type silent chain along the inner circumference thereof, which comprises a meshing element having teeth formed on an outer circumference thereof for meshing engagement with meshing teeth of link plates of the chain which are oriented inwardly with respect to the chain, two buffer-ring support elements each having a cylindrical outer surface and provided concentrically on opposite sides of the meshing element, and two buffer rings each having an inside diameter larger than the outside diameter of the buffer-ring support elements and each being floatingly fitted around the cylindrical outer surface of one of the buffer-ring support elements while the buffer rings are prevented from moving in the axial direction relative to the corresponding buffer-ring support elements. The buffer rings each have an outer peripheral surface adapted to be in abutment with opposing flat back faces of link plates at positions in front and in rear of a meshing position at which the meshing teeth of the link plates are in mesh with the meshing teeth of the meshing element. At the meshing position, the outer peripheral surface of each of the buffer rings is separated from the flat back faces of the link plates and an inner peripheral surface of each of the buffer rings is in abutment with the cylindrical outer surface of one of the buffer-ring support elements.
When the sixth-type sprocket is used for meshing with the double-meshing-type silent chain along the inner circumference thereof, the outer peripheral surfaces of the buffer rings disposed on opposite sides of the meshing element are first brought into abutment with the flat end faces of the link plates of the chain.
When the back faces of the link plates impinges on the outer peripheral surfaces of the buffer rings, the buffer rings are flexed or otherwise deformed in a floating manner around the buffer-ring support members to thereby absorb impact energy created at a collision. Thereafter, as the chain advances, the meshing teeth of the outermost link plates of each link reach the meshing position, the outer peripheral surfaces of the buffer rings disengage from the back faces of the link plates. At the meshing position, the inner peripheral surfaces of the buffer rings abut on the cylindrical outer surfaces of the buffer-ring support elements.
As the chain further advances, the outer peripheral surfaces of the buffer rings come again into abutment with the opposing back faces of the link plates and guide the chain such that the engagement between the meshing teeth of the meshing element and the meshing teeth of the corresponding link plates is released.
The sixth-type sprocket has substantially the same advantageous effects as those of the fifth-type sprocket described above.